1. Field of the Invention
The invention relates to an exerciser, more particularly to an exerciser with a friction-type resistance device.
2. Description of the Related Art
Referring to FIG. 1, a conventional ski exerciser is shown to comprise a base (A) with front and rear ends, and a pair of parallel guide rails (B) disposed on the base (A) and extending from the front end to the rear end of the base (A). A pair of driven units (C), such as pedals, are mounted slidably and respectively on the guide rails (B). Each of a pair of lever arms (D) has a bottom end connected pivotally to the front end of the base (A). A friction-type resistance device of the conventional ski exerciser includes a pair of guide rollers (E), an endless transmission belt (F), a friction wheel (G) and a friction belt (H).
Each of the guide rollers (E) has a vertically oriented axis and is mounted rotatably on a respective one of-the front and rear ends of the base (A) between the guide rails (B). The endless transmission belt (F) is trained around the guide rollers (E) and has two mounting portions secured respectively to the driven units (C). The friction wheel (G) is secured coaxially to a bottom surface of the guide roller (E) at the front end of the base (A). The friction belt (H), which may be a woven belt, is trained on a peripheral portion of the friction wheel (G).
When the user's feet drive the driven units (C) to slide reciprocatingly along the guide rails (B), the transmission belt (F) moves to drive rotatably and alternatingly the guide rollers (E) in clockwise and counterclockwise directions. The friction wheel (G) rotates with the guide rollers (E), thereby resulting in friction between the friction wheel (G) and the friction belt (H) for resisting movement of the driven units (C). This illustrates how an exercise effect is achieved when the conventional ski exerciser is in use.
FIG. 2 illustrates the connection between the friction wheel (G) and the friction belt (H) in greater detail. As illustrated, the friction belt (H) has a first end connected to the base (A) and a second end connected to a first end of a tension spring (I). The second end of the tension spring (I) is connected to a threaded shank of an adjustment unit (K) via a flexible strip (J). The adjustment unit (K) is mounted threadedly on the base (A) and is operable so as to adjust the tension of the friction belt (H) or the tightness of contact between the friction belt (H) and the friction wheel (G). The tension spring (I) permits even distribution of the tension force of the friction belt (H) therealong.
When the friction wheel (G) rotates in the direction indicated by the arrow (M), the friction belt (H) experiences a force in the compressing direction of the tension spring (I). In this case, constant frictional contact between the friction belt (H) and the friction wheel (G) is ensured. However, when the friction wheel (G) rotates in the opposite direction indicated by the arrow (N), the friction belt (H) experiences a force in the pulling direction of the tension spring (I). In this case, the tension spring (I) expands and contracts intermittently, thereby resulting in poor frictional contact between the friction belt (H) and the friction wheel (G).
In order to overcome the above drawback, it has been proposed that the tension spring (I) be removed, and that the second end of the friction belt (H) be connected directly to the threaded shank of the adjustment unit (K). However, if the tension force in the friction belt (H) is too large, the static friction force between the friction belt (H) and the friction wheel (G) would make it very difficult to operate the driven units (C). On the other hand, if the adjustment unit (K) is operated so as to reduce the tension force in the friction belt (H), a clearance might be formed between the friction belt (H) and the friction wheel (G) and thus, no friction force for resisting the movement of the driven units (C) will be generated.